1. Field of the Invention
This invention relates to a monophase electromagnetic rotary actuator which may find particular application in controlling valves.
2. Discussion of the Background
Actuators having a rotor and a stator structure have, in particular, been described in French patent No. 89.08.052 of the applicant. These actuators are optimized for considerable travels, close to the limit, which in theory is 180 degrees for actuators having two poles and in practice is on the order of 120 degrees, and for actuators having four poles, 90 degrees in theory and on the order of 60 degrees in practice.
For applications requiring travels between 60 degrees and 120 degrees, and a considerable torque, previously known actuators, however, exhibit several drawbacks, in particular because of their weight and their bulk.
In particular, for certain applications, a person skilled in the art selects hybrid-type stepper motors and not the monophase motors of the prior art. Such motors are of a biphase type and generally have about fifty poles. These motors exhibit an advantage of a high torque/mass ratio. On the other hand, these motors require complex control electronics, which increases their overall cost and reduces their reliability. Furthermore, the functional air gaps for these stepper motors, are less than a tenth of a millimeter, which involves very reduced assembly and production tolerances, and puts a strain on the price and reliability of such actuators.